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IR Maser Offers First CW Coherent-Light Source

Coherent-light communication systems appear significantly closer to realization with news of a cw infrared maser developed at Bell Telephone Laboratories, Murray Hill, N.J. The device, employing a mixture of helium and neon, delivers a principal output of 15 mw at 1.153 microns. Minimum line width is reportedly 10 kc, and beam spread is less than 1 min of arc.

The gas-discharge principle used in this first cw source of coherent light could prove applicable in a wide variety of gases and gas mixtures, according to Bell scientist Dr. Ali Javan, inventor of the device. Dr. Javan also indicated that later versions of gas discharge masers might operate at wavelengths as short as 5,000 Å. Such a "green" maser would be of considerable interest to Navy scientists who believe that a transmission "window" in sea water at about 5,000 Å may permit submarine detection by a form of light radar.

The maser is pumped by a 28-mc signal applied to a 10-to-1 helium-neon mixture in a slender glass tube. Helium atoms excited by the signal transfer their energy to the neon atoms through a collision process, thereby creating an excess of neon atoms at a higher level.

This energy is then surrendered by maser radiation as the neon atoms return to a lower energy level. Since the collision process is relatively efficient and the total of atoms involved is small, the principle lends itself to cw operation with a pumping source of reasonable size. (Electronic Design, Feb. 15, 1961, p. 20)

This achievement of continuous laser operation was a significant development and opened new vistas for communications. Following this announcement were a flood of other groups achieving cw operation with the HeNe laser. (Note that the Bell Labs device was still called an optical maser rather than a laser.)